Diabetes mellitus is the most common of endocrine disorders, and is characterized by inadequate insulin action. Diabetes mellitus has two principal variants, known as Type I diabetes and Type II diabetes. The latter is also referred to as DM/II (diabetes mellitus type II), adult-onset diabetes, maturity-onset diabetes, or NIDDM (non-insulin dependent diabetes mellitus).
Type II diabetes generally develops in adulthood, and the risk of development of Type II diabetes increases with age. Factors such as obesity also contribute to the risk. A patient suffering from Type II diabetes secretes insulin, but the insulin's target cells are less sensitive to insulin. Symptoms of Type II diabetes are typically slow to appear, and a patient having Type II diabetes may not be aware of his condition. A blood test may show whether the patient has impaired glucose tolerance (IGT), which is often a precursor to Type II diabetes, or compensated Type II diabetes. Unless addressed with treatment such as diet and exercise, these conditions may develop into uncompensated Type II diabetes, a very serious condition.
Patients at risk for diabetes may use a glucose sensor. Most glucose sensors presently in common use are based on electrochemical methods such as the electroenzymatic method where blood glucose is oxidized under glucose-oxidase control, producing gluconic acid and hydrogen peroxide. Alternately, the produced gluconic acid can be determined directly. Both of these sensor types, however, suffer from stability problems. Optical glucose sensors have been tried, but optical sensors may not be feasible for long-term continuous monitoring or for implantable applications.
Poor diet and lack of exercise may not only increase the risk of Type II diabetes, but may increase the risk of heart disease as well. Obesity may, for example, contribute to high blood pressure, which increases the workload of the heart. In addition, the risk of coronary heart disease, like the risk of developing Type II diabetes, increases with age.
In commonly-assigned U.S. Pat. No. 5,741,211 to Renirie, et al., a possible relationship between diabetes mellitus and coronary heart disease was discussed. A correlation between electrocardiogram (ECG) changes and blood glucose was described, and systems and methods were described whereby changes in blood insulin could be monitored as a function of ECG signals. The system applied signal processing to the continuously sensed ECG signals to discriminate selected portions such as the QRS complex and the T-wave. The discriminated portions may be further processed to determine a relationship between the signal and the patient's blood insulin and/or blood glucose levels. The '211 patent is hereby incorporated by reference herein in its entirety.
Long-term monitoring systems and devices known in the art typically involve chemically based sensors. These sensors are typically not medically or economically beneficial for a patient who may be at risk of developing diabetes. Examples of these techniques and/or devices may be found in the issued U.S. Patents listed in Table 1 below.
TABLE 1U.S. Pat. No.InventorIssue Date5,660,163Schulman et al.Aug. 26, 19975,999,848Gord et al.Dec. 7, 19996,081,736Colvin et al.Jun. 27, 20006,119,028Schulman et al.Sep. 12, 20006,175,752 B1Say et al.Jan. 16, 20016,212,416 B1Ward et al.Apr. 3, 20016,221,011 B1BardyApr. 24, 20016,259,937 B1Schulman et al.Jul. 10, 20016,277,072 B1BardyAug. 21, 20016,360,888 B1McIvor et al.Mar. 26, 2002
All patents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention.